Inductive coupling, often called magnetic coupling, couples magnetic energy from one coil to another coil. Inductive coupling may be used in transformers to change a voltage on a primary coil (also called a winding) to a higher or lower voltage on a secondary coil. For example, high voltage power lines use transformers to “step down” high voltages on power lines to lower voltages (e.g. 120 volts) that may be used in homes. Transformers may be used to isolate one electrical system from another electrical system.
The transfer of energy can be more efficient if a magnetic medium such as iron is used. However, energy may be transferred through a medium such as air from one coil to another coil. Because inductive coupling does not need an electrical conductor to transfer energy from one coil to another coil, batteries in electronic devices may be charged without requiring an electrical cord to be attached to the electronic device. For example, many electric toothbrushes use inductive coupling to recharge batteries in the electrical toothbrushes. These electric toothbrushes are charged by simply placing them on a stand that contains a source of magnetic energy.
Inductive coupling may be used to transfer electrical power as in the case where high voltage transformers transfer power from high voltage power lines to homes. In addition to transferring power, inductive coupling may be used for communication. For example, a transformer may be used to transfer an analog signal (e.g. an audio signal) from an amplifier to a loudspeaker in order to produce sound. In addition, digital signals may be transmitted from one coil to another coil in order to facilitate communication.
Inductive coupling may be used to transfer power and transmit information concurrently. For example, backscatter modulation is a method of communicating in an inductively coupled system where power is transferred from the power transmitter to the power receiver and information is communicated from the power receiver back to the power transmitter. When inductive coupling is used to transfer power and transmit information concurrently, the transfer of power may corrupt the transmission of information. For example, in a system using backscatter modulation, the charging of a battery can create digital pulses that are transmitted from a receiver to the transmitter corrupting data that is communicated from the receiver to the transmitter.